Cold resistant cellular rubber



Patented June 2, 1953 COLD RESISTANTKJELLULAR RUBBER William U. Hohwieler, Morrisville,Pa., assignor to-the UnitedStates of America-as represented by the Secretar-yof the Army N Drawing. ApplicationMarch 17., 1952, Serial No. 277;095

(organ-724) vltzzQlai ns. .1

The present invention relates, JtzO, ea could-resistant cellular rubber composition.

*More particularly, the present :invention arelates to a cellular, sponge-like rubber ecomnosition with low temperature equalities, :suchttiiat its highly resilient properties .are .maintained a a temperature of '65:F.,Jandin some casesas low as 85F.' The rubber coinpo sitionmayrbe made in numerous colorssuch as pure white, olive drab, black, etc, by the addition of Ini ments without any deleterious vefiecton thellow temperature resilient properties oithetrubber.

Periscopes, direct sighting telescopes and elbow telescopes for guns mounted onmilitary vehicles such as tanks, motor carriages, field artillery, anti-aircraft artillery etc, are usually provided with head and eye rests in order to protect the man at-the sight from :excess vibrations when the 'vehicleand gun are being used. -Previo.usly these head and eye rests :have been made -:by using horse hair-padding covered with leather. In additionto the susceptibility of the leather to attack by fungi, :the construction has .proved unsatisfactory sincethe hair has .a-tendencynto pack down hard and 1 become solid, especially at low temperatures, and to labsorbmoisture :in the pores which when it"ireezes causes the leather to become brittlexandtherefore to crack.

"Head and .eye rests-made o1": sponge .-.rub'oer have also :been tried and found wanting since the open-pore construction of the :rubber and the myriad canals and cracks interconnecting the pores make the rubber extremely absorbent .With the result that decreasing temperatures and subsequent freezing of the ,moisture .in the pores cause loss .of resiliency, '.'loss of .flexibility, increase in hardness anfdfinally brittleness.

Cellular rubber is notopen to the aboveobjections. "In cellular rubber each hole or pore is surrounded by rubber. There is anabsence of interconnecting channels or canals between the pores, and the entire structure presents an essentially non-porous or closed-cell condition, hence the rubber is comparatively non-absorbent, and is therefore free of internal ice formation resulting in loss of resiliency, which isicharacteristic of the open-celled, porous sponge-rubber.

Cellular rubber has been produced experimentally by others. However, the end result has not been satisfactory since diiliculty hasbeen experienced in making the blowing agent utilized, compatible with the sulfur added for mil.-

canization, and still retain the necessary cell I construction required for the production of effective cold-resistant cellular rubber. Additionally the prior art product has been found .to be lumpy, and the cell walls have been oval and 0f non-uniform thickness with consequentloss in 1 as follows.

her structure which iSiIZBSiSt31'1tit0 extremely. .cold

(temperature and which retains its resiliency and zisjoftness when subjected to ":such cold temperaure.

.It is alsonan objecttoi this invention to .disclose a, composition cellular rubber structure :Which .will stand upiiioria period .ofaapproxi-mately :72 hours eat :3t6032F., and which will also withstand, forat 'leastiitirhours iextremelyzcoldtemtionable loss of resiliency'and softness, and withvzen-tithe rtendencyrof the rubber duo become rtacky,

crack orv become n=brittle..

It is also .afurther object of this invention to produce a cellular rubber composition which:is

essentially .DQH-IIOIEOIIS andlssubstantially i-nonabsorbent, andwtherefore :Eree ofsinternalicaformation= at .low temperatures.

The following ..description BS6138 forth in'ldetail the process steps employed initheiformul-ation of cellular rubber ..:according "to the :zobj ects :lbe-

fore-mentioned. Eightiormulations were tried,

four of :theiormulations utilizing :similar .steps ,with' substantially the sameringre'd'ients in varying proportions. .remaiim'ng riour :formulations were composed ;by mixing -;difierent .pro- :por-tions offfour :previons: formu-lations. The end product in each .case was white 2 cellular .irubber, although it is to the understood llthat :difierent colors icould be zlOhllail'lfld abya-adding the required pigmentation at thEZI- QDBI time.

In the preparationiofseachcof:the formulations manyof the;chemicals andsmaterials usedxarea of :a proprietary mature, "and preparatory 'to :designating the "proportions ;of each chemical required, a list of :the .rproprletary "items :by trade name sandiby-chemical composition will be given.

The list :Eollows:

Trade Name of x Materiul R. P. A. #3 36.5%b xylyl Mercaptan+63.5% inert Hydrocar on. Retarder W Salicylic acid with a dispersing agent. -U1;ucel N. D 40% lDlllllJlOSO Pentamethylenatetramine+60% inert filler.

Titanium'd'ioxl' e.

Polymerof buteues, sopolymerized astoproduce a synthet c, rheavylbodied oil'like product. Butyl :Qlarbitol lfxlrmaL-a high molecular weight polyether havlngthe chemical formula, Cilia- OGgH OCbHsOCH2QC2H4OC2H4OIC H The actual .processingof the formulationsis flale Crepe .is broken down and masticated" bylzplacing sheets :0f the material in amill whichgessentially comprises two steeland cast :iron cylindrical .rollerspeach-about I6 inches indiameter and 42 inches long.

centages.

preferred to crude rubber direct from the plantation, or smoked sheet, owing to its greater degree of uniformity.

During the breaking down process, R. P. A. #3-

days, to prevent spoilage due to setting of the material, since to hold it longer may destroy its ability to be blown into the desired cellular form.

After the mixture of rubber and R. P. A. #3 has cooled sufficiently, the other ingredients are introduced one by one with the exception of sulfur, which is not added until the mixture is thoroughly blended and mixed into the proper consistency. This blending usually takes about 30 minutes, the operator stopping the treatment when sampling indicates proper texture and freedom from lumps. Premature addition of sulfur may generate heat during the mixing operation and start the vulcanization process too soon, therefore it is expedient to add the sulfur last to obtain maximum results in the production of cellular rubber.

After the mixing and blending and the addition of sulfur, the resulting mass is placed in a mold press where heat to vulcanize and to mold the rubber is applied. Heat is applied slowly since the heating causes the blowing agent to throw off gas, and experience indicates that if gas escapes too rapidly, cellular formation is inhibited or prevented entirely.

The eight formulations are listed below. For the first four formulations the first column indicates the number of pounds of each ingredient, and the second column represents the proportion of each ingredient in terms of per- For conveniencethe trade names are used rather than the chemical identity of the various materials in each mixture.

As previously indicated the Pale Crepe supplies the required rubber base, whereas R. P. A. #3 is used to break down and soften the rubber before the other ingredients are added. Stearic acid and Vistac #1 assist in the plasticizing,

4 additionally the stearic acid is required to insure vulcanizing action of the zinc oxide and Altax. Rayox is merely a whitening agent whereas T. P. 90-3 is a low temperature plasticizer which is 5 responsible for producing a compound which will retain its softness when subjected to temperature of from 65 F. to 85 F.

The Unicel N. D. and Retarder W are usually added together. Unicel N. D. is the blowing 1o agent which inflates the cells and produces the cellular construction, however if added without the Retarder W, vulcanization may proceed at a too rapid rate. The Retarder W slows up vulcanization and permits the rubber to rise and inflate before vulcanization is effective at temperaturesof from 187 F. to 200 F. Altax will not vulcanize without the presence of sulfur, whereas sulfur alone is too slow as a vulcanizer, however the combination of sulphur and Altax, as is well known, provide for rapid vulcanization. In producing cellular rubber, the step of vulcanization is very critical and therefore the proportioning of Altax and sulfur must be given special attention.

Tuex is also a vulcanizing agent, which in action is much faster than the combination of sulfur and Altax. In instances where intricate molds are required, this ingredient may be omitted, in order to allow the cells to rise better before the vulcanizing effect takes place,

and at the same time give the rubber a chance to flow out into the intricate molds. Formulation No. 4 is a mixture in which Tuex has been omitted. This formulation was found to be extremely effective in molding periscope head rests,

utilizing pounds of steam pressure or an approximate temperature of 330 F. for a vulcanizing period of approximately minutes.

The term cellular rubber herein is applied to mean rubber in which each cell, hole or pore presents a closed-cell condition, in contradistinction to sponge rubber presenting an openpore condition including myriad canals and channels interconnecting the pores or holes.

Although the present invention has been described in conjunction with preferred proportions and weights of ingredients, it is to be understood that variations in proportions may be resorted to without departing from the spirit 50 and scope of the invention, as those skilled in the art will readily understand. Such variations are considered to be within the purview'and scope of the invention and the appended claims.

Formulation 1 2 3 4 Wt., Per- Wt., Per- Wt., Per- Wt., Per- Lbs. cent Lbs. cent Lbs. cent Lbs. cent Pale Crepe 20. 00 57. 85 20.00 56. 68 10.00 55. 17 20.00 55. 08 R. P. A. #3 .06 0.17 .06 0.17 .03 0.17 .06 0.17 Sulphur 45 1. 30 45 1. 27 225 1. 24 45 l. 24 Stearic Acid .20 0.58 .20 0.57 30 1.66 1. Zinc Oxide 1.74 60 1.71 50 2. 76 1. 00 2. 0.58 .20 0. 57 20 1.10 40 1. l0 2. 96 l. 70 4. 83 85 4. 70 l. 70 4. 68 0.06 .02 0. 06 01 0.06 10 0.28 0.06 .02 0.06 01 0.06 11.57 4. 00 11.36 2.00 11. 02 4. 00 11 02 5.78 2.00 5.68 1.00 5.51 2.00 5.51 17. 35 6.00 17. 04 3.00 16. 55 6. 00 16. 52

Total 34. 57 100. 00 35. 25 100. 00 18. 100.00 36. 31 100.00

Formulation 5: 1 part No. 2 to 4 parts No. 3. Formulation 6: 4 parts No. 2 to 3 parts N0. 3.

to each 77 pounds of No 2 Formulation 8: Small but effective amount not exceeding 1 pound of Retarder W to each pounds of N0. 3.

I claim: 1. A cold resistant cellular rubber product of a composition containing 55 to 58% of Pale Crepe, up to 0.2% of a mixture of xylyl mercaptan with .inert hydrocarbon; 1.2% to 1.3% sulfur; 0.50%

to 1.70% stearic acid, 1.70% to 2.80% zinc oxide; 0.50% to 1.10% salicylic acid with a dispersing agent; 2.90% to 4.90% dinitroso pentamethylenetetramine with an inert filler; up to 0.3% 2,2 benzothiazyl disulfide, up to 0.1% tetramethyl thiuram disulfide, 11.0% to 12% titanium dioxide, 5.0% to 6.0% of a polymer of butenes so polymerized as to produce a synthetic, heavy-bodied oil-like product, and 16.0% to 18.0% of a high molecular weight polyether having the chemical formula Gel-IsO92H4OC2H4OCH2OC2HeOC2I-I4OC4H9 2. The composition in claim 1 wherein said mixture of xylyl mercaptan with inert hydrocarbon contains 36.5% and 63.5% of each material respectively, and wherein dinitroso pentamethylenetetramine with inert filler consists of 40% of the former and 60% of the latter.

3. A cold resistant cellular rubber product of a composition containing 57.85% Pale Crepe; 0.17% of a mixture of xylyl mercaptan with inert hydrocarbon; 1.3 sulfur; 0.58% stearic acid; 1.74% zinc oxide; 0.58% salicylic acid with dispersing agent; 2.96% dinitroso pentamethylenetetramine with an inert filler; 0.06% 2,2 benzothiazyl disulfide; 0.06% tetramethyl thiuram disulfide; 11.57% titanium dioxide, 5.78% of a polymer of butenes so polymerized as to produce a synthetic, heavy bodied, oil-like product, and 17.35% of a high molecular weight polyether having the chemical formula 4. The composition of claim 3 wherein said mixture of xylyl mercaptan with inert hydrocarbon contains 36.5% and 63.5% of each material respectively, and wherein dinitroso pentamethylenetetramine with inert filler consists of 40% of the former and 60% of the latter.

5. A cold resistant cellular rubber product of a composition containing 56.68% Pale Crepe; 0.17% of a mixture of xylyl mercaptan with inert hydrocarbon; 1.27% sulfur; 0.57% stearic acid, 1.71% zinc oxide; 0.57% salicylic acid with a. dispersing agent; 4.83% dinitroso pentamethylenetetramine with an inert filler, 0.06% 2,2 benzothiazyl disulfide; 0.06% tetramethyl thiuram disulfide; 11.36% titanium dioxide; 5.68% of a polymer of butenes so polymerized. a to produce a synthetic, heavy bodied oil-like product, and 17.04% of a high molecular weight polyether having the chemical formula 6. The composition of claim 5 wherein said mixture of xylyl mercaptan with inert hydrocarbon contains 36.5% and 63.5% of each material respectively, and wherein dinitroso pentamethylenetetramine with inert filler consists of 40% of the former and 60% of the latter.

7. A cold resistant cellular rubber product of a composition containing 55.17% Pale Crepe; 0.17% of a mixture of xylyl mercaptan with inert hydrocarbon; 1.24% sulfur; 1.66% stearic acid; 2.76% zinc oxide; 1.10% salicylic acid with a dispersing agent; 4.70% dinitrosc pentamethylenetetramine with an inert filler; 0.06% 2,2 benzothiazyl disulflde; 0.06% tetramethyl thiuram disulfide, 11.02% titanium dioxide, 5.51% of a polymer of butenes so polymerized as to produce a synthetic, heavy bodied oil-like product, and

16.55% of a high molecular Weight polyether having the chemical formula 8. The composition in claim 7 wherein said mixture of xylyl mercaptan with inert hydrocarb-on contains 36.5% and 63.5% of each material respectively, and wherein dinitroso pentamethylenetetramine with inert filler consists of 40% of the former and 60% of the latter.

9. A cold cellular resistant rubber product of a composition comprising 55.08% Pale Crepe; 0.17% of a mixture of xylyl mercaptan with inert hydrocarbon, 1.24% sulfur; 1.65% stearic acid; 2.75% zinc oxide; 1.10% salicylic acid with dispersing agent, 4.68% dinitroso pentamethylenetetramine with an inert filler; 0.28% 2,2 benzothiazyl disulfide; 11.02% titanium dioxide, 5.51% of a polymer of butenes so polymerized as to produce a synthetic heavy-bodied oil-like product; and 16.52% of a high molecular weight polyether having the chemical formula 10. The composition in claim 9 wherein said mixture of xylyl mercaptan with inert hydrocarbon contains 36.5% and 63.5% of each material respectively, and wherein dinitroso pentamethylenetetramine with inert filler consists of 40% of the former and 60% of the latter.

11. A cold resistant cellular rubber product of a composition comprising 55 to 58% of Pale Crepe, up to 0.2% of a mixture of xylyl mercaptan with inert hydrocarbon, 1.2% to 1.3% sulfur, 0.50% to 1.7% stearic acid, 1.70% to 2.8% Zinc oxide, 0.50% to 1.10% salicylic acid with a dispersing agent, 2.90% to 4.90% dinitroso pentamethlyenetetramine with an inert filler, up to 0.3% of 2,2 benzothiazyl disulfide, 11.0% to 12% titanium dioxide, 5.0% to 6.0% of a polymer of butenes so polymerized as to produce a synthetic, heavy-bodied oil-like product, and 16.0 to 18.0% of a high molecular weight polyether having the chemical formula.

12. A cold resistant cellular rubber product of a composition comprising 55 to 58% of Pale Crepe, up to 0.2% of a mixture of xylyl mercaptan with inert hydrocarbon, 1.2% to 1.3% sulfur, 0.59% to 1.7% stearic acid, 1.70% to 2.8% zinc oxide, 0.50% to 1.10% salicylic acid with a dispersing agent, 2.90% to 4.90% dinitroso pentamethylenetetramine with an inert filler, up to 0.3% of 2,2 benzothiazyl disulfide, not more than 0.1 tetramethyl thiuram, 11.0% to 12% titanium dioxide, 5.0% to 6.0% of a polymer of butenes so polymerized as to produce a synthetic, heavybodied oil-like product, and 16.0 and 18.0% of a high molecular weight polyether having the chemical formula C4I'I9OC2H4OC2H4OCH2OC2H4OC2H4OC4H9 WILLIAM U. HOHW'IEIER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,218,167 Harkins Oct. 15, 1940 2,491,709 Briggs Dec. 20, 1949 2,534,883 Smyers Dec. 19, 1950 2,544,483 Baum Mar. 6, 1951 2,602,784 Taylor July 8, 1952 OTHER REFERENCES Unicel ND, Dupont, Report No. 47-3, May 1947, by L. S. Bake, pages 1 to 4.

Thiokol Facts, March 1944, page 11. 

1. A COLD RESISTANT CELLULAR RUBBER PRODUCT OF A COMPOSITION CONTAINING 55 TO 58% A PALE CREPE, UP TO 0.2% OF A MIXTURE OF XYLYL MERCAPTAN WITH INERT HYDROCARBON; 1.2% TO 1.3% SULFUR; 0.50% TO1.70% STEARIC ACID 1.70% TO 2.80% ZINC OXIDE; 0.50% TO 1.10% SALICYLIC ACID WITH A DISPERSING AGENT; 2.90% TO 4.90% DINITROSO PENTAMETHYLENETETRAMINE WITH AN INERT FILLER; UP TO 0.3% 2,2 BENZOTHIAZYL DISULFIDE, UP TO 0.1% TETRAMETHYL THIURAM DISULFIDE 11.0% TO 12% TITANIUM DIOXIDE, 5.0% TO 6.0% OF A POLYMER OF BUTENES SO POLYMERIZED AS TO PRODUCE A SYNTHETIC, HEAVY-BODIED OIL-LIKE PRODUCT, AND 16.0% TO 18.0% OF A HIGH MOLECULAR WEIGHT POLYETHER HAVING THE CHEMICAL FORMULA 